Removed RestClientXML class

After unifying RestClient class to handle both container
types - json and xml, class RestClientXML becomes redundant.

Change-Id: I1bcf5e4df130b8eee26d0abcf1741ba3ea8f3d00
Partially-implements: bp refactor-rest-client
diff --git a/tempest/services/compute/xml/extensions_client.py b/tempest/services/compute/xml/extensions_client.py
index f97b64d..3e8254c 100644
--- a/tempest/services/compute/xml/extensions_client.py
+++ b/tempest/services/compute/xml/extensions_client.py
@@ -15,14 +15,15 @@
 
 from lxml import etree
 
-from tempest.common.rest_client import RestClientXML
+from tempest.common import rest_client
 from tempest import config
 from tempest.services.compute.xml.common import xml_to_json
 
 CONF = config.CONF
 
 
-class ExtensionsClientXML(RestClientXML):
+class ExtensionsClientXML(rest_client.RestClient):
+    TYPE = "xml"
 
     def __init__(self, auth_provider):
         super(ExtensionsClientXML, self).__init__(auth_provider)